Flow soldering process and apparatus

ABSTRACT

There is provided a flow soldering process for mounting an electronic component onto a board by a solder material, which process is appropriate for using a lead-free solder material as the solder material. 
     In the flow soldering process, thermal efficiency of flow soldering is improved in preheating step and/or solder material supplying step thereof. In one aspect of the present invention, a heating cover is located above a preheater, and the flow soldering is conducted while the board passes between the heating cover and the preheater. In another aspect of the present invention, a gap between a preheater and a solder bath is 20 to 60 mm. In yet another aspect of the present invention, a distance between a primary wave and a secondary wave is not larger than 60 mm.

TECHNICAL FIELD

The present invention relates to a flow soldering process for mounting acomponent(s) such as an electronic component(s) onto a board (orsubstrate) by means of a solder material, and also relates to anapparatus for such process.

BACKGROUND ART

A flow soldering process utilizing a molten solder material in the formof a wave(s) has been conventionally known as one of processes forconnecting an electronic component or the like to a board in the fieldof production of an electronic circuit board. Such flow solderingprocess generally includes a flux applying step for applying flux onto aboard, a preheating step for heating the board in advance, and a soldermaterial supplying step for supplying a solder material to the board bycontacting the board with a wave(s) of the solder material. Hereinafter,the conventional flow soldering process will be described with referenceto the drawings. FIG. 15 is a schematic side view of the conventionalflow soldering apparatus while showing its internal construction. FIG.16 is a schematic view of the flow soldering apparatus of FIG. 15 whenviewing it from a cross section taken along an X′—X′ line.

At first, a board is supplied with flux by a flux supplying means (notshown) while applying the flux onto a lower surface of the board. Theboard is, for example, a printed circuit board onto which an electroniccomponent such as a “through hole insertion component (or an insertedcomponent)” (i.e. a component a part of which is inserted into a throughhole, for example, a discrete component or a lead component) is to bemounted at a predetermined position according to a known manner. Theflux generally contains an active ingredient such as rosin (a resincomponent) as well as a solvent such as isopropyl alcohol. The fluxapplying step for applying such flux to the board is conducted in orderto improve wettability and a spreading property of the solder materialon a surface of a land formed on or through the board (i.e. a portion tobe supplied with the solder material) by removing an oxide film (anaturally oxidized film) which is unavoidably formed on the land. As theflux supplying means (or device), a spray fluxer for spraying the fluxin the form of mist to the board, a foam fluxer for contacting the boardwith the flux in the form of foam or the like can be used. These fluxsupplying means can be situated separately from a flow solderingapparatus 60 of FIG. 15, though the flux supplying means can form theflow soldering apparatus 60 by integrally incorporating the fluxsupplying means in the flow soldering apparatus 60.

The board 71 applied with the flux as described above is then fed intothe flow soldering apparatus 60 shown in FIG. 15 through an inlet 61thereof. The board 71 is mechanically conveyed in a direction of anarrow 62 (hereinafter referred to as a conveyance direction) inside theapparatus 60 (along the conveyance line shown as a broken line in FIG.15) at a substantially constant speed. More specifically, the conveyanceof the board 71 is conducted by holding the board 71 with conveyancefingers 72 a and 72 b at its both edge portions which locate on opposedright and left sides of the board when viewing the board towards theconveyance direction 62 as shown in FIG. 16 and by mechanically movingthe conveyance fingers 72 a and 72 b in the conveyance direction of thearrow 62. The conveyance fingers 72 a and 72 b are connected to chains74 a and 74 b respectively and run around conveyer frames 73 a and 73 brespectively in a plane parallel to a principal plane of the board 71.The conveyer frames 73 a and 73 b extend from the inlet 61 to an outlet69 shown in FIG. 15. The conveyer frame 73 a is a base conveyer framewhich is fixed, and the conveyer frame 73 b is a width adjustableconveyer frame which can slide in directions being perpendicular to theconveyance direction and able to keep parallel to the fixed conveyerframe 73 a (in other words, which directions are shown as a left andright arrow in FIG. 16 and lateral in the sheet of FIG. 16).

The board 71 conveyed in the apparatus 60 from the inlet 61 toward theoutlet 69 as described above is firstly heated by a preheater 63locating under the conveyance line of the board, for example a farinfrared heater. Such heating step is referred to as a preheating step.The preheating step is conducted for vaporizing and removing anunnecessary solvent ingredient in the flux applied onto the board 71through the above described flux applying step so as to leave only theactive ingredient on the board 71 and also for preheating the board 71prior to supply of a solder material 64 to the board 71 so as toalleviate a heat shock of the board 71 upon contacting the board 71 witha molten solder material 64. The preheater 63 is located under theconveyance line by generally being put on a bottom of a channelstructure (or support) 76 which is open on its upside and which isconnected to the fixed conveyer frame 73 a and a fixed frame 75 at itstop portions. Thus, the preheater 63 heats the board 71 from a lowerside of the board 71 which is the same side to which the solder materialis supplied in the following solder material supplying step.

The board 71 is subsequently conveyed above a solder material supplyingmeans (or unit) 66 which includes a solder bath 65. The solder bath 65contains the solder material 64 which is in a molten state by heatingbeforehand. A distance “d₁” between the preheater 63 and the solder bath65 (i.e. a distance along the conveyance direction between them) isgenerally about 70 to 150 mm. When the board 71 goes over the soldermaterial supplying means 66, the board 71 is contacted at the lowersurface of the board 71 with a primary wave 67 and a secondary wave 68of the solder material 64, so that the solder material 64 is supplied tothe board 71. As the solder waves 67 and 68 are shown in FIG. 17 whileenlarging them, a distance “d₂” between the primary wave 67 and thesecondary wave 68 (more specifically, a distance along the conveyancedirection from a position at which a certain point of the board 71leaves the primary wave to a position at which the certain point beginsto contact with the secondary wave) is generally about 80 to 150 mm.

In this solder material supplying step, the solder material 64 which issupplied in the form of the primary wave 67 rises in an annular spacebetween a land portion and a lead 74 of the through hole insertioncomponent 73 from a lower side of the board 71 by the capillaryphenomenon as shown in FIG. 18, wherein the land portion forms a wall ofthe through hole 72 perforated through the board 71 and the lead hasbeen inserted through the through hole from an upper side of the board.An excess amount of the solder material 64 adhering to the lower surfaceto the board 71 by the primary wave is removed by subsequentlycontacting the solder material 64 in the form of the secondary wave 68with the board 71. Then, the solder material which is supplied andadheres to the board 71 solidifies with a drop in its temperature andforms a so-called “fillet” as a connection portion of the soldermaterial.

In such solder material supplying step (or flow soldering step), theprimary wave 67 is directed for sufficiently wetting a surface of theland 75 which covers the wall of the through hole 72 (as well as wettingthe lead 74 of the electronic component) with the solder material andfor supplying the solder material into the through hole 72. If it isinsufficient, the solder material does not rise up along the annularspace between the lead 74 and the land portion which forms the wall ofthe through hole 72, so that there occurs a problem of a so-called “redeye (or non-wetting)” (which is referred to as “akame” in Japanese), forexample. The “red eye” is, in other words, a phenomenon in which theland which is generally made of copper shows its color and the land isobserved like as a red colored eye since an annular land portionlocating on the upper surface of the board is not covered with thesolder material but exposed, and the “red eye” may also be referred toas an “insufficient rising (or insufficient wetting up)” (shortage ofthe supply of the solder material to the through hole resulting frominsufficient rising of the solder material by the capillary action). Onthe other hand, the secondary wave 68 is directed for removing an excessamount of the solder material which is adhering to an area of the lowersurface of the board covered with a solder resist and also forconditioning the fillet form. If the removing and conditioning isunsatisfactory, the solder material remains on an area between lands andsolidifies thereon to undesirably form a so-called “bridge” (such bridgeis undesirable since it causes a short circuit) or a ceratoidprojection.

The lead of the electronic component is electrically and physicallyconnected to the land of the board by the fillet of the solder materialas described above. The resultant board 71 is thereafter taken outthrough the outlet 69 (see, FIG. 15). Thus, an electronic circuit boardis produced wherein the electronic component has been soldered to theboard according to the flow soldering process.

For the electronic circuit board produced as described above, an Sn—Pbbased solder material which contains Sn and Pb as main constituents (orcomponents), especially an Sn—Pb eutectic solder material is commonlyused. However, lead contained in such an Sn—Pb based solder material maycause environmental pollution if it is subjected to an inadequate wastetreatment, so that a solder material containing no lead, i.e. aso-called lead-free solder material, has started to be used as analternative of the solder material containing lead in an industrialscale.

However, when the flow soldering is conducted by utilizing theconventional process and apparatus just while substituting the lead-freesolder material for the Sn—Pb based material, there arise a problem thatan occurrence ratio of the so-called “red eye” (or “insufficientrising”) or “bridge” is increased compared with using the Sn—Pb basedmaterial. Therefore, it is not necessarily appropriate in the case ofusing the lead-free solder material to utilize the conventional flowsoldering process and apparatus just as they are.

SUMMARY OF THE INVENTION

The present invention is directed to solve the prior art problems asdescribed above. The present invention aims to provide a flow solderingprocess for mounting an electronic component onto a board with a soldermaterial, which is appropriate to a case of using a lead-free soldermaterial as the solder material, and can alleviate and preferably solveat least a part of the problems as described above. The presentinvention also aims to provide an apparatus for performing such flowsoldering process.

The inventors have found that one cause for the above problems residesin a higher melting point of the lead-free solder material compared withthat of the Sn—Pb based material. Further, we also found that though thelead-free solder material generally has a higher melting point than thatof the Sn—Pb based material, an operation temperature of the flowsoldering using the lead-free solder material is not increased comparedwith an operation temperature of the conventional flow soldering usingthe Sn—Pb solder material by a certain extent which corresponds to thedifference between the melting points of the lead-free solder materialand the Sn—Pb based solder material.

As to the melting points of the general lead-free solder material, it isabout 220° C. for an Sn—Ag—Cu based material, and about 227° C. for anSn—Cu based material. These melting points are higher than that of theSn—Pb eutectic solder material of 183° C. by about 30 to 50° C. On theother hand, the operation temperature of the flow soldering processusing the lead-free solder material is about 250 to 255° C., andincreased by only about 10 to 15° C. from the conventional operationtemperature for the Sn—Pb based solder material of about 235 to 245° C.(The operation temperature as one measure in the present specificationis a liquid temperature of the molten solder material in the solderbath.)

It can be considered that wettability of a molten metal materialgenerally depends on a temperature difference on a basis of a meltingtemperature of the metal material (in other words, a temperaturedifference obtained by subtracting the melting temperature of the metalmaterial from an actual temperature of the metal material in the moltenstate), and the wettability becomes lower as the temperature differencebecomes smaller. Based on this consideration, the wettability of thelead-free solder material is seems to be lower than the wettability ofthe Sn—Pb solder material since the temperature difference bysubtracting the melting temperature from the operation temperature inthe case of using the lead-free solder material is smaller than whenusing the Sn—Pb based material.

By the way, the actual temperature of the solder material variesdepending on the situation in which the solder material is located, andthe actual temperature is highest when the solder material is in themolten state in the solder bath and thereafter decreases by contactingthe solder material in the form of a solder wave with the board having alower temperature thereby losing an amount of heat of the soldermaterial through the board. Though the temperature decrease in the caseof using the Sn—Pb based solder material would be to such an extent thata problem is not caused, the temperature decrease in the case of usingthe lead-free solder material will remarkably influence its wettabilitythereby to inhibit the molten lead-free solder material supplied by theform of the primary wave from sufficiently rising in an annular spacebetween a lead and a land portion which forms a wall of a through holeand therefore causing the so-called “red eye”.

Further in the case of using the lead-free solder material, it can beconsidered that the molten solder material supplied by the primary waveand adhering to the board loses an amount of its heat through the boardand/or an ambient atmosphere before the board make contact with a freshsolder material by the secondary wave, and therefore decreases itstemperature to partially solidify. Such a temperature decrease in thecase of using the Sn—Pb based solder material does not cause a problem.In the case of using the lead-free solder material, however, the soldermaterial will be sensitively influenced by a small temperature decreaseduring a period after leaving the primary wave of the board beforecontacting with the secondary wave, so that the solder material startsto solidify during this period. Since solder material has solidifiedduring the period after leaving the primary wave before contacting withthe secondary wave (in other words, while a certain point of the boardpasses through a distance “d₂” shown in FIG. 17), the solidified soldermust be melted again by the secondary wave. If the solder material isnot sufficiently melted by the secondary wave, this may causes aso-called “bridge” to be formed.

As described above, one cause of the problems of the “bridge”, the“insufficient rising” and so on which may occur in the flow solderingprocess using the lead-free solder material resides the fact that thesolder material supplied to the board decreases its temperatureexcessively relative to its high melting point by losing an amount ofits heat through the board during the flow soldering process, especiallyin a solder material supplying step.

In order to eliminate such cause and avoid the occurrence of the“insufficient rising”, the “bridge” and so on of the solder materialresulting from the temperature decrease of the solder material uponsoldering, it might be suggested to further increase the operationtemperature of soldering in the case of using the lead-free soldermaterial so as to make a temperature difference between the operationtemperature and the melting temperature of the solder material similarto that in the conventional case which uses the Sn—Pb based soldermaterial. However, it is impossible to further increase the operationtemperature while using the conventional apparatus because of constraintof heat resistance as to the board, the components and so on.

Therefore, for the purpose of decreasing an occurrence ratio of the“insufficient rising”, the “bridge” and so on, we have further studiedsuppressing the temperature decrease of the solder material in thesolder material supplying step of the flow soldering process.

The temperature decrease of the solder material, as described above,seems to be caused by losing an amount of heat from the solder material(more specifically, the solder material supplied by the form of theprimary wave) through the board and the ambient atmosphere surroundingthe board. Thus, we have conceived that the occurrence ratio of the“insufficient rising”, the “bridge” and so on which may be caused in theflow soldering using the lead-free solder material can be lowered, forexample, by improving thermal efficiency in a preheating step before thesolder material is supplied to the board so as to maintain a temperatureof the board itself higher (or to suppress the temperature decrease ofthe board), or by suppressing the temperature decrease of the soldermaterial which has been supplied to the board by the form of the primarywave.

On the basis of such knowledge, we have developed a flow solderingprocess improved by various approaches as well as an apparatus for suchflow soldering process.

It is noted that the temperature of a board means a temperature of alower surface of the board, more specifically a temperature of a landportion located on the lower surface (or a back side) of the board. Suchtemperature can be measured by, for example, contacting a thermocouplewith the land portion located on the lower surface of the board (forexample by bonding it to the land portion) and recording data obtainedfrom the thermocouple. Thus, the temperature decrease of the board canbe calculated based on the obtained data.

More specifically, there are provided various flow soldering processesand apparatuses as described below based on the present invention.According to those flow soldering processes and/or apparatus, theoccurrence ratio of the “insufficient rising”, the “bridge” and so onupon the flow soldering can be maintained at an extent which is notlarger than that in the conventional case of using the Sn—Pb basedsolder material.

In one aspect of the present invention, there is provided a flowsoldering process for mounting an electronic component onto a board bymeans of a solder material, which process includes: a preheating stepfor previously heating the board, which is provided with the electroniccomponent and conveyed, by using a preheater locating under the boardand a heating cover extending over the board; and a solder materialsupplying step for supplying the solder material in a molten state tothe board by contacting the solder material as a primary wave and asuccessive secondary wave with a lower surface of the board. It is notedthat a device (or heater) is herein referred to as the preheater, whichdevice previously heats the board prior to the solder material supplyingstep by heating the board from its lower side while locating under theboard as in the conventional apparatus.

In another aspect of the present invention, there is provided a flowsoldering apparatus for mounting an electronic component onto a board bymeans of a solder material, which apparatus includes: a preheaterlocating under the board which is provided with the electronic componentand conveyed; a heating cover locating above the preheater so as toextend over (or cover the above of) the board; and a solder materialsupplying means (or unit or device) for supplying the solder material ina molten state to the board by contacting the solder material as aprimary wave and a successive secondary wave with a lower surface of theboard, the means locating downstream of the preheater in a direction ofconveyance of the board.

In the preheating step prior to the solder material supplying step inthe conventional process as shown in FIGS. 15 and 16, heating of theboard 71 by the preheater 63 such as a far infrared heater locatingunder the conveyance line of the board 71 was conducted in such acondition that a preheating zone which is a part of a conveyance space(that is, a space through which the board 71 is conveyed) and whichlocates above the preheater 63 (wherein such preheating zone is also aspace inside the channel structure 76 (see, FIG. 16)) is notsubstantially isolated form a space outside the channel structure 76 andcommunicated with this space through an opening at a top of the channelstructure 76. The board 71 is exposed to a preheating atmosphere gaswhich is formed by heating an atmosphere gas in the preheating zone bythe preheater 63. In this process, however, an amount of heat of thepreheating atmosphere gas escapes and scatters into an ambient gasoutside the channel structure 76 having a temperature lower than that ofthe preheating atmosphere gas.

According to the process or an apparatus of the present invention, onthe other hand, the preheater locating under the board (or theconveyance space or the conveyance line of the board) and the heatingcover extending over the board (or closing a top of the conveyance spaceor above the conveyance line of the board) are used, so that thepreheating atmosphere gas in the preheating zone between the preheaterand the heating cover is isolated from the ambient gas outside thepreheating zone having the lower temperature to suppress heatdissipation of the preheating atmosphere gas, which results in improvedthermal efficiency. Thus, the board can be heated to a highertemperature because of the higher thermal efficiency according to theprocess or the apparatus of the present invention described above evenwhen an amount of heat supply is equal to that in the conventionalprocess.

Furthermore, the “heating cover” used for the process or the apparatusof the present invention as described above has a function of heatgeneration for heating in addition to the function as the cover forisolating the preheating atmosphere gas to some extent as describedabove. Therefore, it is possible to heat the board not only from itslower side by means of the preheater but also from its upper side bymeans of the heating cover (or a heat generation cover) having thefunction to emit heat. Thus, the board can be heated to a temperaturefurther higher than that in the conventional process using only thepreheater.

As a results of these, it is possible to heat the board in thepreheating step to the temperature higher than in the conventional caseand in turn to transfer the board having the higher temperature to thefollowing solder material supplying step, and therefore to keep atemperature of the board higher at the beginning of the solder materialsupplying step.

It is noted that the heating cover described above preferably rises thetemperature of the board positively, but it may generate a heat to suchan extent that decrease in the temperature of the board can be preventedcompared with a case without the heating cover. In the heating cover, aheat generation body having the function to emit heat (or a heater) anda cover body may not be integral to form a single body. Preferably, theheating cover described above (more specifically the heat generationbody which constitutes the heating cover) is composed of plural sections(which are preferably located along the conveyance direction), andheating of each section as to heating using such heating cover iscontrolled.

In a preferred embodiment, the heating cover described above extends notonly above the preheater but also above the solder material supplyingmeans so as to cover the board. As shown in FIG. 15, a solder materialsupplying zone which is a part of the conveyance space for the board 71and located above the solder material supplying unit 66 (morespecifically, above the solder material 64 in the solder bath 65) is notcovered by a cover and is communicated with its surrounding space, sothat a heat radiated from the molten solder material and so on escapesand scatters into an atmosphere gas in the surrounding space having alower temperature. On the other hand, since the heating cover extendingover both of the preheater and the solder material supplying unit isprovided as in this preferred embodiment of the present invention, notonly the preheating atmosphere gas in the preheating zone but also theatmosphere gas in the solder material supplying zone between the heatingcover and the solder material supplying unit (more specifically, thesolder material in the solder bath) can be isolated from the atmospheregas surrounding them and having the lower temperature. Thus, the heatdissipation from the solder material supplying zone can be suppressedand therefore the thermal efficiency can be further improved. Thus, thetemperature of the board can be kept higher. In this embodiment, theheating cover preferably heats the board in the solder materialsupplying step (or in the solder material supplying zone) in addition tothe preheating step (or in the preheating zone), wherein the phrase“heats the board” includes prevention of the temperature decrease of theboard.

In a preferred embodiment, an apparatus of the present invention furtherincludes a forced convection generating means (or device) for forcedlyconvecting (or mixing) the preheating atmosphere gas in the preheatingzone between the heating cover and the preheater. According to thisembodiment of the present invention, since the preheating atmosphere gasheated by the preheater and the heating cover is forcedly convected inthe preheating zone, a temperature of the preheating atmosphere gas canbe made uniformly, and the thermal efficiency of the preheating zone asa whole can be further improved, and the temperature of the board can bemade further higher.

As the forced convection generating means, for example, a fan or a gasblowing means (or device) can be used. The fan can circulate thepreheating atmosphere gas in the preheating zone. As the gas blowingmeans, a compressor can be used which blows a gas such as an air andpreferably nitrogen gas having a temperature of, for example, about 200to 400° C. and supplies it into the preheating zone. When the gasblowing means is used, it is preferable to supply the gas (e.g. gashaving a temperature higher than that of the atmosphere gas in thepreheating zone) into the preheating zone while suctioning theatmosphere gas in the preheating zone.

According to another aspect of the present invention, there is provideda flow soldering process for mounting an electronic component onto aboard by means of a solder material, which process includes: apreheating step for previously heating the board, which is provided withthe electronic component and conveyed, by using a preheater locatingunder the board; and a solder material supplying step for supplying thesolder material in its molten state to the board by contacting thesolder material as a primary wave and a secondary wave successively witha lower surface of the board which has been previously heated, wherein atemperature decrease of the board during a period after havingpreviously been heated in the preheating step before contacting with theprimary wave is not larger than 3° C.

The temperature decrease of the board after during a period after theboard has been heated by the preheater (and a heating cover as describedabove in case) in the preheating step (that is, after the board haspassed a position which is just above a downstream end of the preheater)and before the board comes in contact with the primary wave by thesolder material supplying means in the solder material supplying step isgenerally not greater than about 3° C. and preferably not greater thanabout 2° C. according to a process of the present invention describedabove, though it is about 5 to 20° C. in the conventional process. Sincethe temperature decrease of the board until the board contacts with theprimary wave is made smaller, the temperature of the board at thebeginning of the solder material supplying step becomes higher.

More concretely, the temperature decrease of the board can be made 3° C.or smaller by setting a gap at 20 to 60 mm between the preheater forpreviously heating the board (more specifically, the downstream end ofthe preheater) and a solder bath which contains the solder material inthe molten state and forms the primary wave and the secondary wave whichcontact with the lower surface of the board (more specifically, anupstream end of the solder bath).

Thus, according to other aspect of the present invention, there isprovided a flow soldering apparatus for mounting an electronic componentonto a board by means of a solder material, which apparatus includes: apreheater locating under the board which is provided with the electroniccomponent and conveyed; and a solder material supplying means forsupplying the solder material in its molten state contained in a solderbath to the board by contacting the solder material as a primary waveand a secondary wave successively with a lower surface of the board,wherein the unit locating downstream from the preheater in a directionof conveyance of the board is constructed to have a gap between thepreheater and the solder bath within 20 to 60 mm.

The gap between the preheater and the solder bath is conventionallyabout 100 mm or more. Since the gap in an apparatus of the presentinvention is made narrower than that in the conventional apparatus, atime required for the board to pass the gap is shortened, and thetemperature decrease of the board is lowered when it is conveyed abovethe gap, and therefore the temperature of the board at the beginning ofthe solder material supplying step can be made higher. It is noted thatthe gap having a width of at least about 20 mm is required to prevent anaccident of a short circuit in the preheater.

In a preferred embodiment, the apparatus of the present inventiondescribed above is provided with a closing means (or device or element)for closing the gap between the preheater and the solder bath toobstruct a stream of an atmosphere gas passing through the gap.

In the conventional apparatus, since there is generally a gap betweenthe preheater and the solder bath in order to prevent an accident of ashort circuit as described above while sucking an atmosphere gas in aspace through which the board was conveyed and passed (also, referred toas a “conveyance space”) into an exhaust duct locating above the boardso as to discharge it out in order to remove smoke outside whichgenerates upon vaporization of the flux, an atmosphere gas having atemperature lower than that of the atmosphere gas in the conveyancespace of the board flows into through the gap between the preheater andthe solder bath upwardly from downside of the gap and entered into theconveyance space locating above the gap from outside of the conveyancespace. As a result, a temperature of the board was directly decreased bycontacting the atmosphere gas having the lower temperature with theboard to carry an amount of heat away from the board, or indirectlydecreased by carrying away an amount of heat away from the atmospheregas in the preheating zone and/or in the solder material supplying zone,in which the preheating zone and the solder material supplying zone arelocated upstream and downstream of the gap, respectively. However,according to this embodiment of the present invention, since a stream ofsuch atmosphere gas having the lower temperature is obstructed by theclosing means (or closure) for closing the gap, the temperature decreaseof the board during passing of the board through a space above the gapis further reduced and the temperature of the board at the beginning ofthe solder material supplying step can be made higher.

In yet another aspect of the present invention, there is provided a flowsoldering process for mounting an electronic component onto a board bymeans of a solder material, which process includes: a preheating stepfor previously heating the board, which is provided with the electroniccomponent and conveyed, by using a preheater locating under the board;and a solder material supplying step for supplying the solder materialin its molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board, while an atmosphere gas in a space above the solder materialin the molten state is thermally isolated from a gas which is downstreamfrom the atmosphere gas in a direction of conveyance of the board andhas a temperature lower than that of the atmosphere gas.

In yet another aspect of the present invention, there is provided a flowsoldering apparatus for mounting an electronic component onto a board bymeans of a solder material, which apparatus includes: a preheaterlocating under the board which is provided with the electronic componentand conveyed; a solder material supplying unit for supplying the soldermaterial in its molten state to the board by contacting the soldermaterial as a primary wave and a secondary wave successively with alower surface of the board, the unit locating downstream from thepreheater in a direction of conveyance of the board; and an isolationmeans (or device) for thermally isolating an atmosphere gas in a spaceabove the solder material supplying unit from a gas which is presentdownstream of the atmosphere gas in a direction of conveyance of theboard and has a temperature lower than that of the atmosphere gas.

Generally, an atmosphere gas in the solder material supplying zone isheated by the solder material used in the solder material supplying stepand having a high temperature (as well as by the preheater used in thepreheating step) to a high temperature. According to the process or theapparatus of the present invention as described above, since such anatmosphere gas in the solder material supplying zone having a relativelyhigh temperature is thermally isolated from an atmosphere gas whichlocates downstream of the solder material supplying zone in a directionof the conveyance of the board and which has a temperature lower thanthat of the atmosphere gas in the solder material supplying zone,dissipation of heat of the atmosphere gas in the solder materialsupplying zone is effectively alleviated. Thus, in the solder materialsupplying step, the board can be exposed to an atmosphere gas having ahigher temperature, and a temperature of the board can be made higher.

In a preferred embodiment, the isolation means as described above is anair curtain or a mechanical shutter.

The air curtain is formed by flowing a gas (preferably a gas having ahigh temperature) across the conveyance space (or the conveyance line)of the board. Though air, nitrogen gas or the like can be used as suchgas, the nitrogen gas is preferable. The nitrogen gas has an advantagein that it induces no oxidation of the solder material and/or the landformed in the board and can further improve a wettability of the soldermaterial.

As the mechanical shutter, a shutter which is made of a heat resistantmaterial such as a stainless steel, a rubber or the like and which ismechanically operable to open and close can be used. Such a shutter canbe operated such that the shutter in a closed condition will open whenthe board is conveyed and approaches to the closed shutter and theshutter closes again after the board is passed through the open shutter.

In yet another aspect of the present invention, there is provided a flowsoldering process for mounting an electronic component onto a board bymeans of a solder material characterized in that, in a solder materialsupplying step for supplying the solder material in its molten state tothe board which is provided with the electronic component on its uppersurface by contacting the solder material as a primary wave and asecondary wave successively with a lower surface of the board, a gashaving a high temperature, preferably a temperature of 200 to 400° C.and more preferably of 220 to 280° C., is blown toward the upper surfaceof the board when the board is on the primary wave.

According to this process of the present invention, since the gas havingthe high temperature is blown toward the upper surface of the board whenthe board locates on the primary wave, the temperature decrease of thesolder material is suppressed upon rising of the solder materialsupplied to the board. In a case, since the solder material is heateduniformly, it is possible to assure the wettability of the soldermaterial sufficient to rise along the through hole formed through theboard. Thus, the occurrence ratio of the “insufficient rising”, the“bridge” and so on can be reduced effectively. The phrase “on theprimary wave” in the present specification means on a zone where theboard contacts with the primary wave with respect to a flow direction ofthe primary wave toward the board and the zone may further include anarea shifted upstream or downstream in the conveyance direction withrespect to a cross section which includes the conveyance direction ofthe board (for example, on the secondary wave).

The gas described above may be blown toward the upper surface of thebard at any appropriate angle, for example from right above or obliquelyabove with respect to the board. In a preferred embodiment, the gas isblown toward it at an angle of −60 to +60 degrees with respect to adirection right to the upper surface of the board in a cross sectioncontaining the conveyance direction of the board. In such a case, aprotrusion formed with the solder material which rises through thethrough hole and protrudes from the upper surface of the board can beflattened out over the upper surface of the board (preferably on a land)by a pressure of the blown gas. As a result, the solder material islikely to spread over the upper surface of the board.

It is noted that a value of the “angle” in the specification is based ona direction which is upwardly perpendicular to the upper surface of theboard in the cross section containing the conveyance direction forconveying the board (that is, such upwardly perpendicular directiondefines an angle of zero degree), and the angle value is expressed with“+” sign when the angle is inclined toward upstream in the conveyancedirection of the board and expressed with “−” sign when the angle isinclined toward downstream in the conveyance direction of the board withrespect to the based direction.

Though air, nitrogen gas or the like can be used as the gas blown towardthe board, nitrogen gas is preferable. Nitrogen gas has an advantage inthat it induces no oxidation of the solder material and/or the landformed on the board and can further improve the wettability of thesolder material. Additionally, it is preferable to use a gas which hasbeen heated prior to being blown toward the board, though normal air(i.e. having a normal temperature) can also be used. In the case inwhich the air having a normal temperature is used, since such air isblown toward the board while involving the atmosphere gas around theboard for heating, the gas having a substantially higher temperature isblown toward the board.

In a preferred embodiment, a sensor detects the presence of the board,and the blow of the gas is controlled depending on a detected result ofthe sensor so as to blow the gas when the board locates on the primarywave. In such embodiment, for example, when a plurality of the boardsare conveyed intermittently, it is possible to reduce an amount of thegas blown toward the board and thereby to reduce power needed to blowthe gas.

In another preferred embodiment of the present invention, there isprovided a flow soldering apparatus for mounting an electronic componentonto a board by means of a solder material, which apparatus includes: asolder material supplying unit for supplying the solder material in itsmolten state to the board, which is provided with an electroniccomponent on its upper surface, by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board; and a blowing means (or device) for blowing a gas, preferablynitrogen gas having a high temperature, preferably 200 to 400° C. andmore preferably 220 to 280° C. toward the upper surface of the boardwhen the board locates on the primary wave. In a preferred embodiment,the blowing means blows the gas toward the upper surface of the board atan angle of −60 to +60 degrees, preferably 0 to +60 degrees, withrespect to a direction right to the upper surface of the board in across section containing the conveyance direction of the board. Theapparatus also includes: a sensor for detecting the presence of theboard; and a controller for the blowing device to blow the gas when theboard locates on the primary wave.

In other aspect of the present invention, there is provided a flowsoldering process for mounting an electronic component onto a board bymeans of a solder material characterized in that in a solder materialsupplying step for supplying the solder material in its molten state tothe board, which is provided with the electronic component on the uppersurface, by contacting the solder material as a primary wave and asecondary wave successively with a lower surface of the board, and thatthe primary wave and the secondary wave contact with the board while adistance “d₂” between the primary wave and the secondary wave is notlarger than 60 mm and preferably about 30 to 50 mm and more preferablyabout 40 mm. The phrase “distance between the primary wave and thesecondary wave” in the specification means a distance along which theboard is carried after the board in contact with the primary wave leavesthe primary wave and before the board comes to contact with thesecondary wave.

Conventionally, the distance “d₂” between the primary wave and thesecondary wave is generally about 80 to 150 mm as shown in FIG. 17. Onthe other hand, since the primary wave and the secondary wave are setcloser to the each other at a distance of 60 mm or less as in thepresent invention, the temperature decrease during the period after theboard leaves the primary wave and before the board comes to contact withthe secondary wave can be effectively reduced. Therefore, it can beeffectively suppressed that the solder material supplied in the form ofthe primary wave to the board and adhered thereto in the molten statesolidifies before a fresh solder material is supplied to the board inthe form of the secondary wave. As a result, it is possible toeffectively reduce the occurrence ratios of the “insufficient rising”,the “bridge” or the like when the lead-free solder material is used.Further, it is also possible to reduce an amount of heat energy requiredto melt the solidified solder material once again by the secondary wave.

It is also possible to reduce the temperature decrease of the boardduring the period after leaving the primary wave and before contactingwith the secondary wave to not larger than 50° C. and preferably notlarger than 30° C., for example, by blowing the gas having the hightemperature toward the board by reducing the heat dissipation of theatmosphere gas in the space locating above the solder bath so as to keepthe temperature of the gas, and/or by preheating the board moreeffectively in the preheating step as described above, in addition to bydecreasing the distance between the primary wave and the secondary wave.

In a preferred embodiment of the process of the present invention asdescribed above, dross which stays between the primary wave and thesecondary wave is mechanically discharged as a dross containing material(i.e. as a mixture of the dross and the solder material) between theprimary wave and the secondary wave. In a more preferred embodiment, avegetable oil containing material is added to the dross containingmaterial which is discharged from between the primary wave and thesecondary wave so as to separate the solder material at least partiallyfrom the dross containing material.

Generally, the dross which is an oxide produced through oxidation of thesolder material floats on the surface of the molten solder material.Usually, the dross is periodically removed in the form of the drosscontaining material which contains the dross and the solder materialsince the dross causes quality degradation of a soldering part (fillet)and insufficient soldering. In the case of using the lead-free soldermaterial, such dross is produced in an amount larger than that in thecase of using the Sn—Pb based solder material. When as in the presentinvention, the primary wave and the secondary wave are located closer toeach other than in the conventional apparatus, the dross is likely toaccumulate between the primary wave and the secondary wave and mayoccasionally climb up the surface of the wave countercurrently frombetween the primary wave and the secondary wave toward the top of thewave and adhere to the board. It is concerned that this may badlyinfluence soldering. Thus, when the primary wave and the secondary waveare located closer to each other than the conventional apparatusaccording to the present invention, it is preferable to mechanicallydischarge the dross which stays between the primary wave and thesecondary wave from between the primary wave and the secondary wave asthe dross containing material. Such mechanical (or forced) discharge maybe conducted successively while the flow soldering process is conducted,or intermittently at an interval between the flow soldering process anda next flow soldering process.

Though it is desirable to isolate the dross alone, the dross isgenerally removed in the form of the dross containing material which isa mixture of the dross and the solder material as described above, andas a result, the solder material as a useful component is wastedtogether with the dross. It has been known that the solder material canbe recovered by adding the vegetable oil to the dross containingmaterial to separate and recover the solder material at least partiallyfrom the dross containing material for the purpose of reducing a loss asthe wasted solder material. As to a material containing the vegetableoil as a separating agent which can separate the solder material fromthe dross containing material, for example, Japanese Patent KokaiPublication Nos. H11-245030 and 2000-190073 describe using any one ofsaccharides, cereal grains or flours, bean flours, seed grains orflours, soybean-cake flours, and peanut hull flours, a combinationthereof and the like. It is preferable also in the present invention toseparate the solder material from the dross containing material at leastpartially by adding such separating agent to the dross containingmaterial, and thereby to recover the useful solder material. It is notedthat the contents of those two publications are incorporated herein bythe reference thereto in their entireties.

In other aspect of the present invention, there is provided a flowsoldering apparatus for mounting an electronic component onto a board bymeans of a solder material, characterized in that the apparatus includesa solder material supplying unit for supplying the solder material inits molten state to the board, which is provided with the electroniccomponent on its upper surface, by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board, and that a distance between the primary wave and thesecondary wave is not larger than 60 mm. The apparatus of the presentinvention preferably includes a discharging means (or device) formechanically discharging dross which exists between the primary wave andthe secondary wave as a dross containing material from a positionbetween the primary wave and the secondary wave. More preferably, theapparatus further includes means (or unit or device) for adding amaterial which contains a vegetable oil to the dross containing materialwhich is discharged from between the primary wave and the secondary waveso as to separate the solder material at least partially from the drosscontaining material.

Additionally, the present inventors have made extensive studies andfound a temperature profile which is suitable to conduct the flowsoldering using the lead-free solder material. According to thetemperature profile obtained by us, the board which has been heated (orpreheated) to 120° C.±30° C. (i.e. 90 to 150° C.) of the temperature ofthe board (more specifically, the temperature of a land surface locatedon a lower surface of the board) is contacted with the primary wave atfirst. Next, the temperature of the board is maintained at not less than200° C. during a period from leaving the primary wave of the board tocontacting with the secondary wave of the board. Then, the board iscooled such that the temperature of the board is 150° C.±30° C. (i.e.120 to 180° C.) at a point in time which is “10 seconds” later from apoint in time at which the board leaves the secondary wave.

Such temperature profile can be established by any appropriate manner.The temperature ranges of the board in respective steps as describedabove can be realized by a manner for example as follows. Thetemperature of the board to be contacted with the primary wave can bemade in the range of 120° C.±30° C. by controlling the temperature ofthe preheater and/or by increasing the efficiency of preheating comparedwith that in the conventional case. The temperature of the board duringthe period from leaving the primary wave to beginning to contact withthe secondary wave can be maintained not less than 200° C. by setting adistance between the primary wave and the secondary wave smaller than inthe conventional case, for example by setting the distance at about 60mm or less. The temperature of the board after the board leaves thesecondary wave is lowered by positively cooling the board by means ofany appropriate cooling means (or device) such as a nozzle, an atomizeror the like which contacts a gas, a liquid or a mixture thereof with theboard so as to cool the board. Thus, the temperature of the board can be150° C.±30° C. at a point in time which is 10 seconds later from thepoint in time at which the board leaves the secondary wave.

By keeping and controlling the temperature profile of the board so as tosatisfying those requirements as described above in the flow solderingprocess, it is possible to effectively reduce the occurrence ratios ofthe “insufficient rising” (or the generation of the “red eye”), thegeneration of the “bridge”, and the so-called “lift-off” (that is, aphenomenon in which an edge of a fillet is lifted off a land portionwhich fillet is located on an upper and/or lower surface of the boardand contacted with the fillet). This will be described later on moreparticularly.

The temperature profile described above is appropriate to conduct theflow soldering while selecting a conveyance speed of the board of, forexample, about 1 to 2 m/min. (or about 1.6 to 3.3 cm/sec.). When theboard is conveyed at a speed in such range, a period from leaving theprimary wave of the board to contacting with the secondary wave of theboard can be, for example, 3 to 5 seconds. When the conveyance speed ofthe board is out of such range, it can be readily understood by thoseskilled in the art that the point in time which is “10 seconds” laterfrom the point in time at which the board leaves the secondary wave maybe shifted appropriately depending on the conveyance speed.

The flow soldering processes and the apparatuses for the processes ofthe present invention are described above which are improved withvarious approaches. One of features of those flow soldering processesand the apparatuses of the present invention can be effective when it isused solely, but two or more features are preferably used incombination. These features can be selected in any combination.

Any of these flow soldering processes and apparatuses of the presentinvention is suitable for a case which uses a lead-free solder materialsuch as an Sn—Cu based material, an Sn—Ag—Cu based material, an Sn—Agbased material, an Sn—Ag—Bi based material, an Sn—Ag—Bi—Cu basedmaterial and the like as the solder material. However, the presentinvention is not limited to such, and a lead-containing solder materialsuch as an Sn—Pb based material can also be used.

As the board applicable to the present invention, it is possible to use,for example, a substrate of a paper phenol based material, a glass-epoxybased material, a polyimide film based material, a ceramic basedmaterial or other material. On the other hand, the electronic componentwhich is connected (or soldered) to the board can be a through holeinsertion component (e.g. a semiconductor, a capacitor, a resistor, acoil, a connector and so on) and/or a surface mount component located ona back surface of the board (e.g. a semiconductor, a capacitor, aresistor, a coil and so on). However, these are merely mentioned for aexemplary purpose, and should not be interpreted as any limitation ofthe present invention.

The flow soldering process of the present invention is preferablyincludes a flux applying step using a flux applying means (or unit ordevice), and the flow soldering apparatus of the present inventionpreferably includes the flux applying means. As the flux applying means,it is possible to use any one alone or in combination of a foaming modeflux applying means for contacting foamed flux with the board (e.g. afoam fluxer) and a spraying mode flux applying means for sprayingatomized flux toward the board (e.g. a spray fluxer). For instance, theflux can be applied onto the board by means of the spraying mode meansand thereafter by the foaming mode means or vice versa. The fluxapplying means can be incorporated to integrally constitute the flowsoldering apparatus or separately located from the flow solderingapparatus.

Though the flow soldering processes and the apparatuses according to thepresent invention have been particularly described in the above, thepresent invention generally includes Modes 1 to 39 as follows:

(Mode 1)

A flow soldering process for mounting an electronic component onto aboard by means of a solder material comprising:

a preheating step for previously heating the board by using a preheaterlocating under the board and a heating cover extending over (or coveringthe above of) the board, the board being provided with the electroniccomponent and conveyed; and

a solder material supplying step for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board.

(Mode 2)

A flow soldering process for mounting an electronic component onto aboard by means of a solder material comprising:

a preheating step for previously heating the board by using a preheaterlocating under the board, the board being provided with the electroniccomponent and conveyed; and

a solder material supplying step for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board which has been previously heated, wherein a temperaturedecrease of the board during a period after being previously heated inthe preheating step before contacting with the primary wave is notlarger than 3° C.

(Mode 3)

A flow soldering process for mounting an electronic component onto aboard by means of a solder material comprising:

a preheating step for previously heating the board by using a preheaterlocating under the board, the board being provided with the electroniccomponent and conveyed; and

a solder material supplying step for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board while an atmosphere gas above the solder material in themolten state is thermally isolated from a gas which is downstream of theatmosphere gas in a direction of conveyance of the board and has atemperature lower than that of the atmosphere gas.

(Mode 4)

The process according to Mode 3, wherein a heating cover extending overthe board is further used for previously heating the board in thepreheating step.

(Mode 5)

The process according to any one of Modes 1, 3 and 4, wherein the soldermaterial supplying step comprises having a temperature decrease of theboard during a period after being previously heated in the preheatingstep before contacting with the primary wave not larger than 3° C.

(Mode 6)

The process according to any one of Modes 1 to 5, wherein a temperaturedecrease of the board during a period after leaving the primary wave ofthe board before contacting with the secondary wave of the board is notlarger than 50° C.

(Mode 7)

The process according to any one of Modes 1 to 6, wherein the soldermaterial is a lead-free solder material selected from the groupconsisting of an Sn—Cu based material, an Sn—Ag—Cu based material, anSn—Ag based material, an Sn—Ag—Bi based material and an Sn—Ag—Bi—Cubased material.

(Mode 8)

A flow soldering apparatus for mounting an electronic component onto aboard by means of a solder material comprising:

a preheater locating under the board which is provided with theelectronic component and conveyed;

a heating cover locating above the preheater so as to extend over (orcover the above of) the board; and

a solder material supplying means for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and secondary wave successively with a lower surface of theboard, the means locating downstream of the preheater in a direction ofconveyance of the board.

(Mode 9)

A flow soldering apparatus for mounting an electronic component onto aboard by means of a solder material comprising:

a preheater locating under the board which is provided with theelectronic component and conveyed; and

a solder material supplying means for supplying to the board the soldermaterial in its molten state contained in a solder bath by contactingthe solder material as a primary wave and a secondary wave successivelywith a lower surface of the board, the means locating downstream of thepreheater in a direction of conveyance of the board and beingconstructed to set a width of a gap between the preheater and the solderbath within 20 to 60 mm.

(Mode 10)

A flow soldering apparatus for mounting an electronic component onto aboard by means of a solder material comprising:

a preheater locating under the board which is provided with theelectronic component and conveyed;

a solder material supplying means for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board, the means locating downstream of the preheater in a directionof conveyance of the board; and

an isolation means for thermally isolating an atmosphere gas above thesolder material supplying means from a gas which is downstream of theatmosphere gas in a direction of conveyance of the board and has atemperature lower than that of the atmosphere gas.

(Mode 11)

The apparatus according to Mode 10 wherein the isolation means is an aircurtain or a mechanical shutter.

(Mode 12)

The apparatus according to Mode 10 or 11, further comprising a heatingcover locating above the preheater to extend over (or cover the aboveof) the board.

(Mode 13)

The apparatus according to Mode 8 or 12, wherein the heating coverextends over also the solder material supplying means so as to cover theabove of the board.

(Mode 14)

The apparatus according to any one of Modes 8, 12 and 13, wherein theheating cover is composed of plural sections and each of the sections iscontrolled for heating with the heating cover.

(Mode 15)

The apparatus according to any one of Modes 8 and 12 to 14, furthercomprising a forced convection generating means for forcedly convectingan atmosphere gas in a space between the heating cover and thepreheater.

(Mode 16)

The apparatus according to Mode 15, wherein the forced convectiongenerating means is a fan or a gas blowing means.

(Mode 17)

The apparatus according to any one of Modes 8 and 10 to 16, wherein thesolder material supplying means comprises a solder bath which containsthe solder material in the molten state, and wherein a width of a gapbetween the preheater and the solder bath is within 20 to 60 mm.

(Mode 18)

The apparatus according to Mode 9 or 17, further comprising a closingmeans for closing the gap between the preheater and the solder bath soas to prevent a gas stream from passing through the gap.

(Mode 19)

The apparatus according to any one of Modes 8 to 18, wherein the soldermaterial supplying means is constructed to set a distance between theprimary wave and the secondary wave which contacts with the board notlarger than 60 mm.

(Mode 20)

The apparatus according to any one of Modes 8 to 19, wherein the soldermaterial is a lead-free solder material selected from the groupconsisting of an Sn—Cu based material, an Sn—Ag—Cu based material, anSn—Ag based material, an Sn—Ag—Bi based material and an Sn—Ag—Bi—Cubased material.

(Mode 21)

A flow soldering process for mounting an electronic component onto aboard by means of a solder material characterized in that in a soldermaterial supplying step for supplying the solder material in its moltenstate to the board by contacting the solder material as a primary waveand a secondary wave successively with a lower surface of the board, theboard being provided with the electronic component on the upper surface,and that a gas having a high temperature is blown toward the uppersurface of the board when the board is on a primary wave.

(Mode 22)

The process according to Mode 21, wherein the gas has a temperature of200 to 400° C.

(Mode 23)

The process according to Mode 21 or 22, wherein the gas is blown towardthe upper surface of the board at an angle of −60 to +60 degrees from adirection right to the upper surface of the board in a cross sectionwhich contains a direction of conveyance of the board.

(Mode 24)

The process according to any one of Modes 21 to 23, wherein the gas isnitrogen gas.

(Mode 25)

The process according to any one of Modes 21 to 24, which comprisesdetecting the presence of the board by a sensor and controlling the blowof the gas depending on a detected result of the sensor so as to blowthe gas when the board is located on the primary wave.

(Mode 26)

A flow soldering apparatus for mounting an electronic component onto aboard by means of a solder material comprising:

a solder material supplying means for supplying the solder material inits molten state to the board by contacting the solder material as aprimary wave and a secondary wave successively with a lower surface ofthe board, the board being provided with the electronic component on itsupper surface; and

a blowing means for blowing a gas having a high temperature toward theupper surface of the board when the board is located on the primarywave.

(Mode 27)

The apparatus according to Mode 26, wherein the gas has a temperature of200 to 400° C.

(Mode 28)

The apparatus according to Mode 26 or 27, wherein the blowing meansblows the gas toward the upper surface of the board at an angle of −60to +60 degrees from a direction right to the upper surface of the boardin a cross section which contains a direction of conveyance of theboard.

(Mode 29)

The apparatus according to any one of Modes 26 to 28, wherein the gas isnitrogen gas.

(Mode 30)

The apparatus according to any one of Modes 26 to 29, furthercomprising:

a sensor for detecting the presence of the board; and

a controller for controlling the blowing means to blow the gas when theboard is located on the primary wave.

(Mode 31)

A flow soldering process for mounting an electronic component onto aboard by means of a solder material characterized in that in a soldermaterial supplying step for supplying the solder material in its moltenstate to the board by contacting the solder material as a primary waveand a secondary wave successively with a lower surface of the board, theboard being provided with the electronic component on the upper surface,and that the primary wave and the secondary wave contact with the boardso as to set a distance between the primary wave and the secondary wavenot larger than 60 mm.

(Mode 32)

The process according to Mode 31, wherein dross which exists between theprimary wave and the secondary wave is mechanically discharged as adross containing material from between the primary wave and thesecondary wave.

(Mode 33)

The process according to Mode 32, wherein a vegetable oil containingmaterial is added to the dross containing material which is dischargedfrom between the primary wave and the secondary wave to at leastpartially separate the solder material from the dross containingmaterial.

(Mode 34)

A flow soldering apparatus for mounting an electronic component onto aboard by means of a solder material comprising a solder materialsupplying means for supplying the solder material in its molten state tothe board by contacting the solder material as a primary wave and asecondary wave successively with a lower surface of the board, the boardbeing provided with the electronic component on its upper surface,characterized in that a distance between the primary wave and thesecondary wave is not larger than 60 mm.

(Mode 35)

The apparatus according to Mode 34, comprising a discharging means formechanically discharging dross which exists between the primary wave andthe secondary wave as a dross containing material from between theprimary wave and the secondary wave.

(Mode 36)

The apparatus according to Mode 35, further comprising a means foradding a vegetable oil containing material to the dross containingmaterial which is discharged from between the primary wave and thesecondary wave to at least partially separate the solder material fromthe dross containing material.

(Mode 37)

A flow soldering process comprising contacting a solder material as aprimary wave and a secondary wave successively with a lower surface of aboard which is provided with an electronic component on its uppersurface, characterized by:

contacting the board with the primary wave, wherein the board has beenpreviously heated so as to have a temperature of the board of 90 to 150°C.;

maintaining the temperature of the board not less than 200° C. during aperiod after leaving the primary wave of the board before contactingwith the secondary wave of the board; and

cooling the board such that the temperature of the board is 120 to 180°C. at a point in time which is 10 seconds later from a point in time atwhich the board leaves the secondary wave.

(Mode 38)

The process according to any one of Modes 21 to 25, 31 to 33 and 37,wherein the solder material is a lead-free solder material selected fromthe group consisting of an Sn—Cu based material, an Sn—Ag—Cu basedmaterial, an Sn—Ag based material, an Sn—Ag—Bi based material and anSn—Ag—Bi—Cu based material.

(Mode 39)

The apparatus according to any one of Modes 26 to 30 and 34 to 36,wherein the solder material is a lead-free solder material selected fromthe group consisting of an Sn—Cu based material, an Sn—Ag—Cu basedmaterial, an Sn—Ag based material, an Sn—Ag—Bi based material and anSn—Ag—Bi—Cu based material.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows a side view of a flow soldering apparatus inone embodiment of the present invention;

FIG. 2(a) schematically shows a cross sectional view of a flow solderingapparatus in one example of the embodiment in FIG. 1 taken along lineX—X, and FIG. 2(b) schematically shows a perspective view of a heatingcover which is provided in the flow soldering apparatus shown in FIG.2(a);

FIG. 3 schematically shows a cross sectional view of a flow solderingapparatus in another example of the embodiment of FIG. 1, whichcorresponds to a cross sectional view of the flow soldering apparatus inFIG. 1 taken along line X—X;

FIG. 4 schematically shows a cross sectional view of a flow solderingapparatus in yet another example of the embodiment of FIG. 1, whichcorresponds to a cross sectional view of the flow soldering apparatus inFIG. 1 taken along line X—X;

FIG. 5 shows a schematic graph of a temperature profile of a board whenit is transferred from a preheating step to a solder material supplyingstep in another embodiment of the present invention while comparing atemperature profile in a case of using the conventional flow solderingprocess and apparatus;

FIG. 6 schematically shows a partial cross sectional view of thevicinity of a solder material supplying means of the flow solderingapparatus described with reference to FIG. 5;

FIG. 7 schematically shows a perspective view of the vicinity of asolder receiving box provided in the flow soldering apparatus of FIG. 6;

FIG. 8 schematically shows a partial cross sectional view of thevicinity of a solder material supplying means of the flow solderingapparatus in yet another embodiment of the present invention;

FIG. 9 schematically shows an enlarged view of a portion of a board andits vicinity for explaining a flow soldering process in one embodimentof the present invention when a through hole of the board is located ona primary wave;

FIG. 10 schematically shows an enlarged view of the vicinity of aprimary wave and a secondary wave in a flow soldering apparatus inanother embodiment of the present invention;

FIG. 11 shows a schematic graph of a temperature profile of a board in asolder material supplying step in the embodiment of FIG. 10 whilecomparing a temperature profile in a case of using the conventional flowsoldering process and apparatus;

FIG. 12 schematically shows a perspective view of a solder materialsupplying means provided in a flow soldering apparatus in yet anotherembodiment of the present invention;

FIG. 13 schematically shows a perspective view of a solder materialsupplying means provided in a flow soldering apparatus in yet anotherembodiment of the present invention;

FIG. 14 shows a schematic graph of a temperature profile of a board inyet another embodiment of the present invention;

FIG. 15 schematically shows a cross sectional view of a conventionalflow soldering apparatus;

FIG. 16 schematically shows a cross sectional view of the flow solderingapparatus in FIG. 15 taken along line X′—X′;

FIG. 17 schematically shows an enlarged view of the vicinity of aprimary wave and a secondary wave in the flow soldering apparatus inFIG. 15; and

FIG. 18 schematically shows an enlarged partial view of a board forexplaining a flow soldering process which uses the flow solderingapparatus shown in FIG. 15 when a through hole of the board is locatedon a primary wave.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. It is noted that the embodiments will bedescribed mainly about points different from the conventional flowsoldering process and apparatus.

(Embodiment 1)

A flow soldering apparatus 20 of the embodiment shown in FIG. 1 has aconfiguration similar to that of the conventional flow solderingapparatus which is described with reference to FIGS. 15 to 18, but it isdifferent from the conventional apparatus in that the apparatus of FIG.1 additionally includes a heating cover 10 which is provided to extendover the conveyance line of the board 11 so as to cover an area above ofthe preheater 3 and the solder material supplying means 6 (or so as toclose tops of the preheating zone and the solder material supplying zoneand thereby isolate them from their surrounding spaces). Hereinafter, aflow soldering process for mounting the electronic component onto theboard by using such flow soldering apparatus 20 will be described.

Flux (not shown) is firstly applied onto a lower surface of the board,which is provided with an electronic component(s) appropriately at adetermined position, by using for example a foaming or spraying modefluxer. Thus, resultant board 11 enters the apparatus 20 through theinlet 1, and is mechanically conveyed in the direction of the arrow 2along the conveyance line (shown as a broken line in FIG. 1) from theinlet 1 to the outlet 9. As in the conventional process, the conveyanceof the board 11 is conducted by holding the board 11 with conveyancefingers 12 a and 12 b and moving the conveyance fingers 14 a and 14 b,to which the chains 12 a and 12 b are connected, around the conveyerframes 13 a and 13 b, respectively.

Referring to FIG. 2, the chain 14 a is shown as a “going” chain portionlocated on a side of the conveyer frame 13 a which is aside of the board11 and a “returning” chain portion located on the other side of theconveyer frame 13 a, and the chain 14 b is also shown similarly to thechain 14 a.

In order to make sliding adjustment of the distance between the fingers12 a and 12 b possible depending on the width of the board 11, it ispreferable to use the conveyer frames 13 a and 13 b wherein one conveyerframe 13 a is a fixed base conveyer frame, and the other conveyer frame13 b is a distance adjustable conveyer frame which can slide in adirection perpendicular to the conveyance direction 2 of the board 11while keeping its parallel relationship with the fixed conveyer frame 13a (that is, slide in a left/right direction in the sheet of FIG. 2(a)shown as a left and right arrow in FIG. 2(a)).

It is noted that the fluxer described above may be installed inside theflow soldering apparatus 20. In this case, the board 11 to which theflux has not yet been applied enters into the apparatus 20 through theinlet 1, and the flux is applied to the lower surface of the board 11upstream of the preheater 3 while the board is conveyed.

When the board 11 is then conveyed over the preheater 3 in due course,the board 11 is previously heated (prior to the solder materialsupplying step) in the preheating step from above and below the board byusing the heating cover 10 which extends over the board 11 as well asthe preheater 3 which is located under the board 11, respectively. Byusing such heating cover 10 together with the preheater 3, the heatdissipation of the preheating atmosphere gas in the preheating zonewhich intervenes between the heating cover 10 and the preheater 3 iseffectively alleviated, so that the thermal efficiency of the flowsoldering apparatus 20 can be increased. At the same time, it ispossible to heat the board 11 from not only below the board but alsoabove the board (such heating includes suppression of the temperaturedecrease of the board). Thus, the board 11 can be heated to atemperature higher than in the conventional process. The board 11 whichis heated as described above is subsequently conveyed above the soldermaterial supplying means 6. It is understandable that the board 11 has atemperature higher than in the conventional process at the beginning ofthe solder material supplying step in which the solder materialsupplying means 6 is used, more specifically upon contacting the board11 with the primary wave 7.

It is sufficient that the heating cover 10 is provided so as to close(or cover) the top of the preheating zone, which is positioned above thepreheater 3. The cover extends over the conveyance space through whichthe board 11 is passed along the conveyance line (shown as the brokenline in FIG. 1). For the purpose of further increasing the thermalefficiency, it is preferable to provide the heating cover 10, as in thisembodiments such that it extends over the preheater 3 and the soldermaterial supplying means 6 so as to close further the top of the soldermaterial supplying zone which is positioned above the solder materialsupplying means 6.

Such heating cover 10 is preferably constructed by applying a heatingelement(s) 10 b such as a hot-wire heater to a cover body 10 a which ismade of a transparent material having a sufficient heat resistance suchas a glass and which has a curved cross sectional form, for example ahemicylindrical form. It is possible to visually monitor the inside ofthe apparatus from the outside thereof by selecting the transparentmaterial for the cover body 10 a. The board 11 is conveyed while beingheld with the conveyance fingers 12 a and 12 b as described above, andthere is a possibility of dropping of the board 11 off the fingers 12 aand 12 b, and particularly a fire risk may exist if the board falls onthe preheater 3. However, when the transparent material is used for thecover body 10 a as in this embodiment, an unusual situation of, forexample, dropping of the board 11 can be discovered earlier and theoccurrence of the fire and so on can be prevented.

Additionally, the heating cover 10 can preferably be opened and closedas shown with a broken line in FIG. 2(a) by means of a hinge which islocated in the vicinity of the fixed frame 15 for the purpose of readymaintenance of the flow soldering apparatus 20. Heating covers 18 and19, which are shown in FIGS. 3 and 4, respectively and have a flat plateform may be used in place of the heating cover 10 having thehemicylindrical form. In this case, the heating cover 18 which isslantingly provided (FIG. 3) is more preferable than the heating cover14 which is horizontally provided (FIG. 4) since the inside of theapparatus is readily monitored through the transparent cover body in theformer.

It is preferable that the heating cover 10 (or the heating element 10 b)preferably consists of plural sections aligned in the conveyancedirection as shown in the drawing and the heating temperature of theheating element 10 b in each section is controlled. Further, thepreheater 3 is also preferably divided into sections so as to controlthe heating temperature thereof on each section basis. According to suchconfiguration, heating of the board 11 can be regulated depending onpositions on the conveyance line, so that a desirable temperatureprofile of the board can be obtained while avoiding rapid heating of theboard for example.

In the preheating step in which the heating cover 10 and the preheater 3described above is used, the board 11 is conveyed through a tunnel likestructure in the direction of the arrow 2 (that is, a directionperpendicular to the sheet of the FIG. 2(a) and penetrating the sheetfrom its backside to its front) which structure is formed by the heatingcover 10 and the channel structure 16 provided with the preheater 3 asshown in FIG. 2(a). In the tunnel like structure, a fan 17 is preferablylocated as a forced convection generating device so as to forcedlyconvect an atmosphere gas of the preheating zone between the heatingcover 10 and the preheater 3. The temperature of the atmosphere gas ofthe preheating zone is increased by heating of the heating cover 10 andthe preheater 3. By conducting the preheating step while the atmospheregas of the preheating zone having the increased temperature is forcedlyconvected in the tunnel like structure by means of the fan 17 asdescribed above, the thermal efficiency of the flow soldering apparatus20 can be further increased, and the board can be supplied to thefollowing solder material supplying step with its higher temperature. Itcan be readily understood by those skilled in the art that a positionand a blast rate of the fan 17, a number of the fans and so on can bemodified conformably to the flow soldering apparatus. Alternatively, ameans (or device) for supplying a compressed air can be used as theforced convection generating means in place of the fan 17, and thecompressed air can be discharged into the tunnel like structure throughthe compressed air injecting port which is located at the position ofthe fan 17.

According to the preheating step as described above, the board 11, whichis beforehand heated to the temperature higher than in the conventionalprocess, is subsequently conveyed into and above the solder materialsupplying means 6 shown in FIG. 1 where the solder material supplyingstep is conducted. This step may be as in the conventional process.Specifically, the step is conducted by contacting the lower surface ofthe board 11 with the molten solder material 4 in the form of theprimary wave 7 and the sequential secondary wave 8 which is placed inthe solder bath 5. Then, the board 11 which has experienced the soldermaterial supplying step is taken out through the outlet 9. Thereby theelectronic circuit board is obtained wherein the electronic component ismounted onto the board 11 according to the flow soldering process.

Since the board 11 is heated by the preheating step described above tothe higher temperature than in the conventional process, the temperatureof the board 11 is also higher than in the conventional process at thebeginning of the solder material supplying step, more specifically uponcontacting the board 11 with the primary wave 7. As a result, it ispossible to suppress the temperature decrease of the solder materialwhich is supplied and adhered to the board compared with the temperaturedecrease in the conventional case even when the lead-free soldermaterial is used as the solder material. Thus, the wettability of thesolder material is kept at a sufficiently high extent, and the soldermaterial which is adhered to the board through the primary wave canavoid partially solidifying before the board makes contact with thesecondary wave. Therefore, it becomes possible to effectively reduce theoccurrence ratios of the “insufficient rising”, the “bridge”, and thelike in the electronic circuit board produced by this embodiment whileusing the lead-free solder material as the solder material compared withthose in the electronic circuit board produced by the conventionalprocess and apparatus.

(Embodiment 2)

The flow soldering apparatus of this embodiment is obtained by, in placeof providing the heating cover 10, locating the preheater 3 and thesolder bath 5 closer to each other in the flow soldering apparatus 20 ofthe Embodiment 1 which is described with reference to FIG. 1. Though thegap d₁ between the preheater 3 and the solder bath 5 in the embodimentof FIG. 1 is about 70 to 150 mm similar to the conventional apparatus,such gap d₁ in the flow soldering apparatus of this embodiment is 20 to60 mm.

In the flow soldering process of this embodiment in which the apparatusdescribed above is used, the board is conveyed across the gap describedabove and subjected to the solder material supplying step after theboard has experienced the flux applying step and the preheating stepaccording to a manner substantially the same as in the Embodiment 1(that is, similar to the conventional process) except the heating covercovering above the board. The temperature profile of the board duringthose steps is shown in FIG. 5.

Referring to FIG. 5, the ordinate axis indicates a temperature of theboard (arbitrary unit); the abscissa axis indicates time (arbitraryunit), which axis therefore corresponds to a position of the board onthe conveyance line in the apparatus; the solid line is a temperatureprofile in this embodiment; and the dashed line is a temperature profilein the case of using the conventional flow soldering process andapparatus. In FIG. 5, these temperature profiles are shown so as tooverlaps to each other at the point in time at which the board contactswith the primary wave.

According to the temperature profile of this embodiment shown as thesolid line in FIG. 5, the temperature of the board (that is, thetemperature of the lower surface of the board, more specifically thetemperature of the surface of the land portion which locates on thelower side of the board) starts to decrease at point A₁ where the boardhaving been preheated in the preheating step leaves the above of thedownstream end of the preheater 3. Then, the board contacts with theprimary wave at point B₁ and the temperature of the board rapidlyincreases to a temperature substantially the same as the temperature ofthe molten solder material and maintained at that temperature at top C₁followed by decreasing after the board leaves the primary wave. Next,the board contacts with the secondary wave at point D₁ and thetemperature of the board again rapidly increases to the temperaturesubstantially the same as the temperature of the molten solder materialand maintained at that temperature at top E₁ followed by decreasingafter the board leaves the secondary wave. It should be noted that thetemperature of the body of the board is not increased to such atemperature as at tops C₁ and E₁ since the periods during which theboard contacts with the primary wave and the secondary wave are short,and especially the period for contacting of the board with the primarywave is very short.

The temperature decrease of the board after being (pre)heated in thepreheating step before contacting with the primary wave in thisembodiment is calculated by subtracting the temperature at point B₁ fromthe temperature at point A₁, and this value is about 1 to 2° C. Moreconcretely, in the case of the gap d₁=30 mm, the conveyance speed of theboard of 1.2 m/min., the temperature at point A₁ of about 110° C., andthe temperature of the molten solder material (i.e. the temperature attops C and E) of about 250° C., the temperature of the board at point B₁can be about 109° C. and therefore the temperature decrease betweenpoint A₁ and point B₁ can be about 1° C. Thus, the temperature decreaseof the board between preheating in the preheating step and contactingwith the primary wave can be made not greater than about 3° C. andpreferably not greater than about 2° C.

On the contrary to the above, referring the conventional temperatureprofile shown in FIG. 5 as the dashed line, a period from a point intime at which the board leaves the preheater to a point in time at whichthe board contacts with the primary wave is made longer since the gapbetween the preheater and the solder bath is larger than that in thisembodiment, and therefore the temperature decrease of the board duringthis period becomes larger. The temperature decrease in the conventionalprocess is calculated by subtracting the temperature at point B₁′ fromthe temperature at point A₁′ which is substantially the same as that atpoint A₁, and generally is about 5 to 20° C. More concretely, in thecase of the gap d₁=100 mm, the conveyance speed of the board of 1.2m/min., the temperature at point A₁′ of about 110° C., and thetemperature of the molten solder material (i.e. the temperature at topsC and E) of about 250° C., the temperature of the board at point B₁′ isabout 100° C. and the temperature decrease between point A₁′ and pointB₁′ is about 10° C.

According to this embodiment, the temperature decrease from the point intime at which the board leaves the preheater (that is, after the boardhas passed over the downstream end of the preheater) to the point intime at which the board contacts with the primary wave is smaller thanthat in the conventional case, so that the temperature of the board bodyis also retained at a temperature higher than that in the conventionalcase. As a result, a difference between the temperature of the boardbody and the temperature of the molten solder material which is suppliedto the board becomes smaller, and an amount of heat which the soldermaterial loses through the board after being supplied to the board isreduced. Thus, the temperature decrease of the solder material whichadheres to the board can be suppressed.

As described above, it is also possible in this embodiment as inEmbodiment 1 to suppress the temperature decrease of the solder materialwhich is supplied and adheres to the board compared with in theconventional case even when the lead-free solder material is used as thesolder material, so that similar effects as in Embodiment 1 can also beobtained. Thus, the flow soldering process and the apparatus of thisembodiment are also suitable for using as the solder material thelead-free solder material as described above, and it becomes possible toeffectively reduce the occurrence ratios of the “insufficient rising”,the “bridge”, and the like.

Additionally, the apparatus of this embodiment preferably includes aplate member 21 shown in FIG. 6 as a closing element for closing the gapbetween the preheater 3 and the solder bath 5 to obstruct a gas streampassing through the gap. The gap between the preheater and the solderbath is generally provided for avoiding possible formation of a shortcircuit as to the preheater when the solder material 4 occasionallyspills over from the solder bath 5 by some external factor and contactswith the preheater 3. Further, an ambient gas in the conveyance space ofthe board is generally suctioned upwardly and discharged through anexhaust duct in order to removing smoke which is generated by vaporizingof a solvent contained in the flux. By providing the plate member 21 toclose the gap, it is avoidable that a gas having a low temperature inthe outside of the conveyance space passes through the gap between thepreheater 3 and the solder bath 5 upwardly (in a direction of an arrowof a broken line shown in FIG. 6) and flows into the conveyance space.As a result, it is possible to suppress the temperature decrease of theboard which may be caused by the inflow of the gas having a lowtemperature from the outside of the conveyance space, and therefore tomake the temperature of the board at the beginning of the soldermaterial supplying step much higher. Thus, it becomes possible toeffectively reduce the occurrence ratios of the “insufficient rising”,the “bridge”, and the like in the case using the lead-free soldermaterial.

Though such a closing means (the closing means 21) is preferably used incombination with this embodiment, the closing means may be used alonewithout reducing the gap between the preheater 3 and the solder bath 5.In this case, the temperature decrease of the board from preheating inthe preheating step to contacting with the primary wave can be made notgreater than about 3° C. and preferably not greater than about 2° C.Thus, it is possible to make the temperature of the board at thebeginning of the solder material supplying step higher than in theconventional case, and thus to effectively reduce the occurrence ratiosof the “insufficient rising”, the “bridge”, and the like in the caseusing the lead-free solder material.

In the case of using the plate member 21 as described above, it ispreferable to locate a solder receiving container 22 on the plate member21 while utilizing the plate member 21 as a sole plate as shown in FIGS.6 and 7. Referring to FIG. 7, a guide 25 is preferably provided at thetop of the solder bath 5 such that the solder receiving container 22 canreceive the solder material 4 when it spills over, and the solderreceiving container 22 is preferably such that it can be pulled out inthe direction of an arrow 26. If the solder material 4 spills over fromthe solder bath 5 by an earthquake for example, a short circuit may beformed by the solder material 4 which contacts with the preheater 3,which causes a concern of a fire. However, an accident of the fire canbe obviated since the solder material 4 can not contact with thepreheater 3 by locating such solder receiving container 22.Additionally, the solder receiving container 22 is also used forreceiving the dross upon the removal of the dross from the soldermaterial as a routine work, and thereby workability of the removal ofthe dross can be improved. Further, in addition to upstream of thesolder bath 5, it is more preferable to locate a solder receivingcontainer 24 and a plate member 23 downstream of the solder bath 5 whichare similar to those located upstream of the solder bath 5.

Though the process/apparatus of this embodiment have advantages asdescribed above even when they are employed as they are, it ispreferable that they are combined with the process/apparatus ofEmbodiment 1.

(Embodiment 3)

The flow soldering apparatus of this embodiment is obtained by adding anair curtain forming means 27 (FIG. 8) to the flow soldering apparatus 20of the Embodiment 1 which is described with reference to FIG. 1 in placeof providing the heating cover 10. Though cooling means 29 (which willbe described later) are shown in FIG. 8 for cooling the board whichmeans is located downstream of the air curtain forming means whilesandwiching the conveyance line, the cooling means is not necessarilyrequired for conducting this embodiment.

Also, in this embodiment, the flow soldering apparatus as describedabove can carry out the flow soldering process including the fluxapplying step, the preheating step and the solder material supplyingstep similarly to the Embodiment 1 except that the heating cover coversthe above of the board (i.e. similarly to the conventional process), butthere is provided a difference between them by using the air curtainforming means 27 as below.

The air curtain forming means 27 forms an air curtain which functions asan insulation means for thermally insulating an atmosphere gas of thesolder material supplying zone which exists above the solder materialsupplying means 6 from an atmosphere gas of a zone downstream of thesolder material supplying zone in the conveyance direction of the board,wherein the latter atmosphere gas has a temperature lower than that ofthe former one. With the air curtain forming means 27, a gas (preferablynitrogen gas) having a high temperature (preferably about 200 to 400°C.) flows inside a pipe which is provided with a slit (or an aperture)having an appropriate size and shape, and the gas is ejected through theslit of the pipe so as to traverse the conveyance line of the board(shown with a broken line in FIG. 8) which is conveyed in the conveyancedirection 2, so that the air curtain 28 is formed.

Generally, the atmosphere gas of the solder material supplying zone isheated by the preheater 3 used for the preheating step (in the case ofEmbodiment 1, the preheater 3 and the heating cover 10) and the soldermaterial 4 having a high temperature used for the solder materialsupplying step. On the other hand, since the atmosphere gas of the zonedownstream of the solder material supplying zone in the conveyancedirection 2 is less thermally influenced by the solder material 4 and soon, so that the atmosphere gas has the temperature lower than that ofthe solder material supplying zone. Thus, because of a temperaturedifference between the atmosphere gas of the solder material supplyingzone and the atmosphere gas having the lower temperature of the zonedownstream of the solder material supplying zone, an amount of heat ofthe atmosphere gas of the solder material supplying zone escapes anddissipates into the atmosphere gas having the lower temperature.

However, since the air curtain 28 is formed between the atmosphere gasesof the solder material supplying zone and of the zone downstream thereofhaving the lower temperature, it is possible to suppress the heatdissipation of the atmosphere gas of the solder material supplying zoneand keep the temperature of the atmosphere gas of the solder materialsupplying zone higher. Thus, it is possible to make the temperature ofthe board which is exposed to the atmosphere gas of the solder materialsupplying zone higher, and therefore to reduce the occurrence ratios ofthe “insufficient rising”, the “bridge” and the like in the case ofusing the lead-free solder material.

The isolating means such as the air curtain as described above can belocated at any position as long as it locates downstream of a positionat which the board contacting with the secondary wave of the soldermaterial leaves the secondary wave of the solder material. The isolatingmeans is preferably located at a position where the isolating means hasno influence upon the external form (or surface) of the secondary wave.The isolating means can be located so as to isolate the atmosphere gaswhile traversing the conveyance space of the board above the vicinity ofthe downstream end of the solder bath.

Additionally, the flow soldering apparatus of this embodiment isparticularly preferable when it is provided with the cooling means 29such as a fan for blowing a gas, a spray for spraying or ejecting aliquid or the like.

When the lead-free solder material is used as the solder material, thereis caused a problem of the occurrence of the so-called “lift-off”. Forreducing the occurrence ratio of such “lift-off”, it is desirable topositively cool the board after the solder material supplying step asdescribed in Japanese Patent Application No. 2001-241979 which is ownedby the applicant of the present application and which claims a domesticpriority from Japanese Patent Applications No. 2000-249588. It is notedthat the contents of the applications are incorporated herein by thereference thereto in their entireties.

For conducting this cooling step, the board may be blown by a gaspreferably having a low temperature while using, for example, a fan or aspot cooler, or may be sprayed with a liquid by using a spray. Since anatmosphere gas of a cooling zone in which the gas and/or the liquid forcooling exists (that is, a zone for cooling the board which zone islocated downstream of the solder material supplying zone) has atemperature lower than that of the solder material supplying zone whichis immediately upstream of the cooling zone in the conveyance direction,the atmosphere gas of the cooling zone absorbs an amount of heat fromthe atmosphere gas of the solder material supplying zone and lowers atemperature of such gas. By lowering the temperature of the atmospheregas of the solder material supplying zone in the solder materialsupplying step, the temperature of the board in the solder materialsupplying step is also decreased.

However, the decrease in the temperature of the board as described abovecan be suppressed in this embodiment by means of the air curtain 28 soas to thermally isolate the atmosphere gas of the solder materialsupplying zone from the atmosphere gas, which has the lower temperaturethan that of the solder material supplying zone, of the cooling zonewhich is positioned downstream of the solder material supplying zone inthe conveyance direction 2. Thus, it is possible to suppress thetemperature decrease of the board in the solder material supplying stepwhich may otherwise be caused in the case wherein the board is cooledafter the solder material supplying step, and to reduce the occurrenceratios of the “insufficient rising”, the “bridge”, the “lift-off” andthe like in the case of using the lead-free solder material. Further,the thermal efficiency of the apparatus as a whole is increased.

Though the process/apparatus of this embodiment have advantages asdescribed above even when they are employed as they are, it ispreferable that they are combined with the process/apparatus ofEmbodiment 1 and/or Embodiment 2. The combination of all of Embodiments1 to 3 is especially preferable since the temperature decrease of theboard in the solder material supplying step is particularly suppressed.

(Embodiment 4)

The flow soldering apparatus of this embodiment is different from theflow soldering apparatus 20 of the Embodiment 1 which is described withreference to FIG. 1 in that the apparatus of this embodiment is providedwith a blowing means 38 for blowing a gas 39 which has a hightemperature onto the upper surface of the board 11 which is located onthe primary wave of the molten solder material as in FIG. 9, in place ofproviding with the heating cover 10. As the blowing means 38, it ispossible to use a means which is configured such that a gas (preferablynitrogen gas) having a high temperature (preferably about 200 to 400°C.) flows inside a pipe which is provided with a slit (or an aperture)having an appropriate size and shape, and the gas is ejected through theslit of the pipe to blow the upper surface of the board 11 which isconveyed. The blowing means 38 preferably blows the gas 39 uniformlyonto the board 11 over its whole width which is perpendicular to theconveyance direction 2 of the board 11 (i.e. a direction shown in thedrawing as arrow 2) while the board 11 is conveyed under the blowingmeans 38.

Similarly to the conventional flow soldering process, the board 11 whichhas been subjected to the flux applying step and the preheating step isconveyed over the solder material supplying means 6 which supplies thesolder material to the board by contacting the molten solder material 4in the form of the primary wave 7 and the secondary wave 8 with thelower surface of the board 11 successively (see FIG. 1). When thethrough hole 32 of the board 11 is situated on the primary wave 7 in duecourse as shown in FIG. 9, the solder material 4 which is supplied inthe form of the primary wave 7 rises up through an annular space betweenthe lead 34 connected to the electronic component 33 and the part of theland 35 which forms the wall of the through hole 32. At this time,according to the flow soldering process of this embodiment, the gas 39having the high temperature supplies an amount of heat to the board 11,more specifically the land which is formed to cover the through hole 32of the board 11, and/or the solder material 4 which rises up in thethrough hole 32. As a result, it is possible to reduce an amount of heatwhich is taken out of the solder material 4 through the land 35 and theboard 11 when the solder material 4 rises up in the through hole 32, sothat the temperature decrease of the solder material 4 can besuppressed. Thus, the solder material 4 can rises up in the through holesufficiently. Referring to FIG. 9, the gas 39 is preferably blown towardthe board 11 at an angle in a cross section including the conveyancedirection 2 of the board (i.e. in the sheet of FIG. 9), wherein theangle is slanted from the direction Y (shown in the drawing as an arrowY) which is upwardly perpendicular to the upper surface of the board (orits principal surface) by an angle θ (theta)=−60 to +60 degrees (in FIG.9, the angle θ (theta) is shown to be a plus value while slanting towardan upstream-side in the conveyance direction 2). As a result, aprotrusion (or bulge) of the solder material 4 which projects from theupper surface of the board 11 can be flattened over the portion of theland 35, which is located on the upper surface of the board 11, by apressure of the blown gas 39. Therefore, the solder material 4 comes tospread over the surface of the part of the land 35 locating on the uppersurface of the board more readily.

The flow soldering apparatus of this embodiment preferably furtherincludes a sensor 40 for detecting the presence of the board 11 and acontroller 41 for controlling the blowing device to blow the gas 39 whenthe board is situated on the primary wave 7. A position at which thesensor 40 detects the presence of the board 11 may be any appropriateone with considering the conveyance speed of the board 11. Though thesensor 40 is shown to be positioned above a position at which the board11 comes to contact with the primary wave 7 in this embodiment, it ispreferable to position the sensor at the inlet of the apparatus and toblow the gas toward the board when the board reaches the primary wavewhile considering the conveyance speed of the board. According to theflow soldering apparatus of this embodiment, since the blow of the gas39 from the blowing means 38 is controlled by the controller 41depending on a result of the detection of the sensor 40 so as to blowthe gas 39 when the board 11 situated on the primary wave 7, it ispossible to reduce an amount of the used gas 39 for blowing toward theboard 11 and an amount of power which is required to blow the gas.

The board 11 which contacts with the primary wave as described abovethen contacts with the secondary wave 8 (see, FIG. 1) and is taken outthrough the outlet 9 of the flow soldering apparatus as in theconventional flow soldering process and apparatus. Thus, an electroniccircuit board is produced wherein the electronic component has beenconnected by flow soldering.

The flow soldering process and apparatus of this embodiment areappropriate for the case of especially using as the solder material thelead-free solder material as described above, and it is possible toeffectively reduce the occurrence ratios of the “insufficient rising”,the “bridge” and so on. In this case, it is desirable to estimate andcontrol the quality of the lead-free solder material in the solder bath.For this purpose, a sensor for estimating the quality of the lead-freesolder material by comparing a melting property of the solder materialwhich is actually used in the solder bath for the flow soldering with asolder material having a predetermined composition while applying aprincipal of the differential thermal analysis can be used. Such asensor is described in Japanese Patent Application No. 2001-171044 whichclaims domestic priorities from Japanese Patent Applications Nos.2000-168903 and 2000-168904, which are all filed in the name of thepresent applicant. It is noted that the contents of those applicationsare incorporated herein by the reference thereto in their entireties.

(Embodiment 5)

The flow soldering apparatus of this embodiment has a configurationsimilar to the conventional flow soldering apparatus which is describedwith reference to FIGS. 15 to 18, but different from the conventionalapparatus in that the apparatus of this embodiment is constructed so asto have a distance d₂ of about 60 mm or less, preferably about 30 to 50mm, and more preferably about 40 mm between the primary wave 7 and thesecondary wave 8 which are formed by the solder material supplying meansas in FIG. 10. In the conventional flow soldering apparatus as shown inFIG. 17, the distance d₂ between the primary wave 67 and the secondarywave 68 is about 80 to 150 mm. In this embodiment as shown in FIG. 10,on the other hand, an upper part of a guide 44 which defines a flow ofthe secondary wave 8 is positioned closer to a guide 43 which defines aflow of the primary wave 7 so as to have the distance d₂ of the value asdescribed above between the primary wave 7 and the secondary wave 8.

While using such flow soldering apparatus, the board 1 is firstsubjected to the flux applying step and the preheating step as in theconventional flow soldering process, and then subjected to the soldermaterial supplying step using the solder material supplying means asdescribed above. The temperature profile of such board is shown in FIG.11. FIG. 11 corresponds to FIG. 5 which is referenced for describing thetemperature decrease in the case of using the flow soldering process andapparatus of above described Embodiment 2. In FIG. 11, the solid line isthe temperature profile in this embodiment, and the dashed line is thetemperature profile in the case of using the conventional flow solderingprocess and apparatus.

According to this embodiment, as shown with the solid line in FIG. 11,the temperature of the board (that is, the temperature of the lowersurface of the board, more specifically the temperature of the surfaceof the land portion which locates on the lower side of the board) startsto decrease at point A₂ where the board preheated in the preheating stepleaves the above of the downstream end of the preheater 3. Then, theboard contacts with the primary wave at point B₂ so that the temperatureof the board rapidly increases to a temperature substantially the sameas the temperature of the molten solder material and maintained at thattemperature at top C₂ followed by decreasing after the board leaves theprimary wave. Next, the board contacts with the secondary wave at pointD₂ and the temperature of the board rapidly increases again to thetemperature substantially the same as the temperature of the moltensolder material and maintained at that temperature at top E₂ followed bydecreasing after the board leaves the secondary wave.

The temperature decrease of the board after leaving the primary wave andbefore contacting with the secondary wave in this embodiment iscalculated by subtracting the temperature at point D₂ from thetemperature of top C₂ (i.e., the temperature which is substantially thesame as the temperature of the molten solder material). More concretely,in the case of the gap d₂=4-mm, the temperature of the molten soldermaterial (i.e. the temperature of tops C and E) of about 250° C., andthus the temperature of top C₂ of about 250° C., the temperature ofpoint D₂ can be about 160° C. and therefore the temperature decrease canbe about 90° C.

According to the conventional temperature profile shown with the dashedline in FIG. 11, on the other hand, since the distance d₂ between theprimary wave and the secondary wave is larger than in this embodiment,the period after leaving the primary wave and before contacting with thesecondary wave becomes longer, and therefore the temperature decrease ofthe board during such period becomes larger. The temperature decrease inthe conventional process is calculated by subtracting the temperature atpoint D₂′ from the temperature at top C₂′. More concretely, in the caseof the distance d₂=70 mm for example and the temperature of top C₂ ofabout 250° C., the temperature of point D₂′ is about 128° C. andtherefore the temperature decrease is about 122° C. When the temperaturedecrease of such a large value is caused especially in the case of usingthe lead-free solder material, the solder material which adheres to theboard by the primary wave partially solidifies, and this may derives the“insufficient rising”, the “bridge” and so on. According to thisembodiment, it becomes possible to suppress the temperature decrease ofthe board after leaving the primary wave and before contacting with thesecondary wave by setting the distance between the primary wave and thesecondary wave at 60 mm or less. Thus, the solder material which adheresto the board by the primary wave effectively avoids from partiallysolidifying especially in the case of using the lead-free soldermaterial.

As described above, the flow soldering process and the apparatus of thisembodiment are also suitable for using as the solder material thelead-free solder material as described above, and it is possible toeffectively reduce the occurrence ratios of the “insufficient rising”,the “bridge” and so on. Additionally, it is also preferable in thisembodiment to estimate the quality of the lead-free solder material inthe solder bath by means of the sensor as described in Japanese PatentApplications which are already referred to in the above.

Further, it is preferable to combine at least one of the features ofEmbodiments 1 to 4 with this embodiment. The flow soldering apparatus ofthis embodiment is preferably provided with the heating cover asdescribed in Embodiment 1. Though the gap d, between the preheater andthe solder bath may be similar to the gap of the conventional flowsoldering apparatus, the gap is preferably about 20 to 60 mm as inEmbodiment 2 described above. By thermally insulating so as to alleviatethe heat dissipation of the atmosphere gas of the zone located above thesolder bath and/or by effectively preheating the board in the preheatingstep as described above, the temperature decrease of the board can besuppressed furthermore, and it can be reduced to preferably not greaterthan 50° C. and more preferably not greater than 30° C.

(Embodiment 6)

In addition to having the distance between the primary wave and thesecondary wave not larger than 60 mm as in Embodiment 5 which isdescribed above with reference to FIGS. 10 and 11, the flow solderingapparatus of this embodiment shown in FIG. 12 includes a screw 45positioned between the guide 43 for the primary wave and the guide 44for the secondary wave, a motor 46 for rotating the screw 45, acontainer 47 which includes a material containing vegetable oil and isconnected to a line for supplying the material as the separating agent49 into the solder bath, and a valve 48 for controlling the supply ofthe material from the container 47 to the solder bath. The screw 45 andthe motor 46 form a discharging means for mechanically discharging thedross, which accumulates between the primary wave and the secondarywave, as a dross containing material from between the primary wave andthe secondary wave. The container 47 and the valve 48 form a means foradding the vegetable oil containing material to the dross containingmaterial which is discharged from between the primary wave and thesecondary wave.

As to the solder material supplying means shown in FIG. 12, the primarywave (not shown in FIG. 12) flows out from an opening of the guide 43(such as plural apertures as shown in FIG. 12) and runs down over thesurface of the guide 43, and on the other hand the secondary wave (notshown in FIG. 12) flows out from an aperture(s) of the guide 44 (such asan elongated opening as shown in FIG. 12) and run down the surface ofthe guide 44. Though the dross is likely to accumulate between theprimary wave and the secondary wave by selecting the distance of notgreater than 60 mm between the primary wave and the secondary wave as inthis embodiment when compared with the conventional case, theaccumulating dross can be sent out in the form of the dross containingmaterial by mechanically discharging it from between the primary waveand the secondary wave while rotating the screw 45 by means of the motor46. When the separating agent 49 (the vegetable oil containing material)is added to the dross containing material which is thus discharged fromthe container 47 through the valve 48, the solder material is at leastpartially separated from the dross containing material and a drosscontaining material which has an increased content of the dross can beremoved. As a result, a loss of the solder material can be reduced.

As the discharging means for mechanically discharging the dross, whichaccumulates between the primary wave and the secondary wave, as thedross containing material, the screw 45 and the motor 46 are used inthis embodiment. Alternatively, it is also possible to use a platemember 50 which is adapted to a cross sectional shape of the gap formedbetween the guides 43 and 44 and an air cylinder (or a motor) 51 whichreciprocates the plate member 50 between the guide 43 and 44 as shown inFIG. 13. By moving the plate member 50 by the air cylinder 51 from aproximal side to a distal side with respect to the air cylinder 51, thedross accumulating between the primary wave and the secondary wave isforced to move by the plate member 50 and discharged from between theprimary wave and the secondary wave.

Such discharging means as described above may be used alone though it ispreferably used in combination with the means for adding the vegetableoil containing material (the separating agent) as in this embodimentshown in FIG. 12 and in its modification shown in FIG. 13. The dischargeof the dross containing material can be conducted continuously orintermittently as a part of a routine work. Furthermore, it is alsodesirable in this embodiment and its modification to estimate andcontrol the quality of the lead-free solder material in the solder bathby means of the sensor as described in the above with reference to theJapanese Patent Applications.

(Embodiment 7)

This embodiment relates to a temperature profile of the board in theflow soldering process by means of the lead-free solder material. Morespecifically, the board is contacted with the primary wave, wherein theboard has been previously heated (preheated) such that the temperatureof the board is in a range of 120° C.±30° C. (i.e. 90 to 150° C.) beforepoint in time a₀ at which the board comes to contact with the primarywave. Next, the temperature of the board is maintained at not less than200° C. from point in time b₁ at which the board leaves the primary waveto point in time b₂ at which the board comes to contact with thesecondary wave. Then, the board is cooled such that the temperature ofthe board is in a range of 150° C.±30° C. (i.e. 120 to 180° C.) at pointin time c₁ which is 10 seconds later from point in time c₀ at which theboard leaves the secondary wave.

It is noted that a time axis as the abscissa axis of the temperatureprofile in FIG. 14 is inverted from the temperature profiles in FIGS. 5and 11 (that is, apparently, FIG. 14 and FIGS. 5 and 11 are laterallyinverted to each other). In addition, it should be noted that atemperature profile which is shown as the solid line in FIG. 14 ismerely an example of the temperature profile of the board, and that thepresent invention is not limited to this temperature profile.

Though points in time a₀ b₁ b₂ and c₀ of the temperature profiledescribed above depend on a mutual positional relationships among theprimary wave and the secondary wave in the flow soldering apparatus andthe board which is conveyed on them, and the conveyance speed of theboard, points in time a₀ b₁ b₂ and c₀ can be determined based on thetemperature profile which is obtained by measuring the temperature ofthe board. First, point in time a₀ at which the board comes to contactwith the primary wave can be determined as a point in time at which thetemperature of the board first starts to rapidly increase on thetemperature profile. Point in time b₁ at which the board leaves theprimary wave can be determined as a point in time at which thetemperature of the board starts to decease on the temperature profileafter the temperature of the board has been rapidly increased from pointin time a₀ determined as above and kept such increased temperature.Point in time b₂ at which the board comes to contact with the secondarywave can be determined as a point in time at which the temperature ofthe board starts to rapidly increase again on the temperature profileafter point in time b₁ determined as above. And finally, point in timec₀ at which the board leaves the secondary wave can be determined as apoint in time at which the temperature of the board starts to decease onthe temperature profile after the temperature of the board has beenrapidly increased from point in time b₂ determined as above and keptsuch increased temperature.

The temperature profile of this embodiment is appropriate for the caseof setting the conveyance speed of the board at, for example, about 1 to2 m/min. (or about 1.6 to 3.3 cm/min.). In the case where the board isconveyed at a speed in such range, the period after the board leaves theprimary wave and before the board contacts with the secondary wave maybe, for example, 3 to 5 seconds.

The temperature profile of this embodiment is appropriate for the caseof flow soldering by means of the lead-free solder material. If atemperature profile which is generally used in the conventional flowsoldering by means of the Sn—Pb based solder material is applied to thecase of using the lead-free solder material, various soldering defectsmay be occur. However, in the case where the flow soldering is conductedaccording to the temperature profile as in this embodiment, it ispossible to effectively reduce the occurrence ratios of the solderingdefects even when the lead-free solder material is used. Hereinafter,this is explained in detail.

According to the conventional temperature profile which is generallyused for the case of using the Sn—Pb based solder material, the boardwhich is heated to about 70 to 80° C. is contacted with the primarywave. When the electronic component is soldered to the board by applyingthe above to the case of using the lead-free solder material so that theboard having the temperature of about 70 to 80° C. contacts with theprimary wave, there arise problems of the “red eye” caused by that thelead-free solder material can not sufficiently rises up in the throughhole, and of unsatisfactory connection of the solder material betweenthe fillet and the land.

On the other hand, the board is heated in this embodiment such that thetemperature of the board is in the range of about 120° C.±20° C. (i.e.90 to 150° C.) immediately before point in time a₀ at which the boardcontacts with the primary wave. The temperature of the board can be inthe range of 90 to 150° C., for example, by controlling the temperatureof the preheater which is used for preheating the board and/or bycontrolling the thermal efficiency for heating by the preheater whileconsidering conditions such as a flow of the atmosphere gas in which theboard is located during preheating. Since the board is heated to notless than 90° C. in this embodiment as described above, the lead-freesolder material sufficiently rises up in the through hole, and thereforeit becomes possible to obtain a satisfactory connection between thesolder material and the land. On the other hand, since the temperatureof the board is not greater than 150° C. in this embodiment, it is fullyavoidable that the electronic component to be connected (or soldered) tothe board is damaged by heat.

Furthermore, according to the conventional temperature profile which isgenerally used for the case of using the Sn—Pb based solder material,the significant temperature decrease of the board after the board leavesthe primary wave and before the board comes to contact with thesecondary wave occurs, so that the temperature of the board is decreasedto about 100 to 180° C. When this is also applied to the case of usingthe lead-free solder material so as to solder the electronic componentonto the board so that the board of which temperature is decreased tosuch a level is contacted with the secondary wave, various problems maybe encountered. For example, the “bridge” may be caused because the formof the fillet is not well conditioned, the “red eye” may be causedbecause the lead-free solder material does not sufficiently rise up inthe through hole, or the unsatisfactory connection may obtained betweenthe fillet of the solder material and the land.

According to this embodiment, on the other hand, the temperature of theboard can be maintained at or above 200° C. after point in time b₁ atwhich the board leaves the primary wave before point in time b₂ at whichthe board comes to contact with the secondary wave. The temperature ofthe board is the substantially same temperature as that of the soldermaterial in the molten state in the solder bath such as about 250° C.for the period during which the board is in contact with the primarywave (i.e. the period between points in time a₀ and b₁) and for theperiod during which the board is in contact with the secondary wave(i.e. the period between points in time b₂ and c₀). For the period afterthe board leaves the primary wave and before the board comes to contactwith the secondary wave (i.e. the period between points in time b₁ andb₂), the temperature of the board continues decreasing due to releasingits heat into a surrounding atmosphere of the board which atmosphere hasa lower temperature and becomes the lowest in this period generally at apoint in time immediately before the board comes to contact with thesecondary wave (i.e. point in time b₂). In other words, the temperatureof the board immediately before the board comes to contact with thesecondary wave (i.e. point in time b₂) is maintained at or above 200° C.in this embodiment. It is possible to maintain the temperature of theboard not less than 200° C., by making the distance d₂ between theprimary wave and the secondary wave smaller than in the conventionalcase, for example changing the distance d₂ into about 60 mm or less,preferably about 30 to 50 mm and more preferably about 40 mm, or bysupplying an amount of heat from the outside with hot air or the like.As stated above, the temperature decrease of the board after the boardleaves the primary wave and before the board comes to contact with thesecondary wave can be reduced, and the temperature of the board ismaintained at or above 200° C. in this embodiment. Therefore, it isavoidable to form an unsatisfactory connection between the fillet of thesolder material and the land.

Additionally, according to the conventional temperature profile which isgenerally used for the case of using the Sn—Pb based solder material,the temperature of the board is larger than about 200° C. even at apoint in time which is 10 seconds later from the point in time at whichthe board leaves the secondary wave since the board is not positivelycooled after the board leaves the secondary wave. When this is alsoapplied to the case of using the lead-free solder material for solderingthe electronic component onto the board, various problems may beencountered. For example, the “lift-off” which is a specific problem ofthe lead-free solder material may be caused more often, and the “crack”may occur.

According to this embodiment, on the other hand, the board is cooledsuch that the temperature of the board is in the range of 150° C.±30° C.(i.e. 120 to 180° C.) after 10 seconds later on the basis of the pointin time at which the board leaves the secondary wave (i.e. at point intime c₁ which is 10 seconds later on the basis of the point in time c₀).It is possible to cool the temperature of the board to 120 to 180° C.,for example, by contacting air and preferably cold air with the board bymeans of a nozzle, a fan and the like, or by spraying a liquid in theform of mist onto the board by means of an atomizer. By having thetemperature of the board at or below 180° C. at the point in time whichis 10 seconds later from the point in time at which the board leaves thesecondary wave as described above, the occurrence ratio of the“lift-off” can be effectively reduced since segregation of a componentwhich has a relatively low melting point among components of thelead-free solder material can be suppressed. On the other hand, byhaving the temperature of the board at or above 120° C. at the point intime which is 10 seconds later from the point in time at which the boardleaves the secondary wave, the generation of the “crack” in the filletresulting from rapid cooling may be avoidable.

As described above in detail, by controlling the temperature profile ofthe board as in this embodiment, it is possible to effectively reducethe various defects such as the occurrences of the “red eye” (or“insufficient rising” of the solder material), the “bridge”, the“lift-off” and the “crack” which are encountered remarkably in the caseof using the lead-free solder material.

Industrial Applicability

According to the present invention, there is provided flow solderingprocesses for mounting an electronic component onto a board by means ofa solder material, which processes are appropriate for using thelead-free solder material as the solder material as well as apparatusesfor conducting the processes. Those flow soldering processes andapparatuses make it to suppress a temperature decrease of the soldermaterial supplied to the board (optionally a temperature decrease of theboard itself) compared with the conventional case, and thereforeoccurrences of the “insufficient rising”, the “bridge” and so on can beeffectively reduced even though the lead-free solder material is used asa solder material.

The present application claims priorities under the Paris Convention toJapanese Patent Application Nos. 2000-292271 filed on Sep. 26, 2000 andNo. 2000-299423 filed on Sep. 29, 2000 both of which are entitled “FLOWSOLDERING PROCESS AND APPARATUS”. The contents of those applications areincorporated herein by the references thereto in their entireties.

What is claimed is:
 1. A flow soldering process for mounting anelectronic component onto a board with a solder material, the processcomprising: preheating the board by using a preheater located under theboard, the board being provided with the electronic component and beingconveyed; and supplying the solder material in its molten state to theboard by successively contacting a lower surface of the board, which haspreviously been heated, with a primary wave of the solder material and asecondary wave of the solder material, wherein a temperature decrease ofthe board during a period after being previously heated and beforecontacting the primary wave is not larger than 3° C.
 2. The flowsoldering process according to claim 1, wherein a heating coverextending over the board is used for preheating the board.
 3. The flowsoldering process according to claim 1, wherein the solder material is alead-free solder material selected from the group consisting of an Sn—Cubased material, an Sn—Ag—Cu based material, an Sn—Ag based material, anSn—Ag—Bi based material and an Sn—Ag—Bi—Cu based material.
 4. The flowsoldering process according to claim 1, wherein the temperature decreaseis of a portion of the board, and the period is from a time point atwhich the portion of the board leaves the preheater for the primary waveto a time point at which the portion begins to contact the primary wave.5. A flow soldering apparatus for mounting an electronic component ontoa board with a solder material, the apparatus comprising: a preheaterlocated under the board which is provided with the electronic componentand conveyed; and a solder material supplying unit for supplying asolder material, contained in a solder bath, to the board in a moltenstate by successively contacting a lower surface of the board with thesolder material as a primary wave and a secondary wave, the soldermaterial supplying unit being located downstream of the preheater in adirection of conveyance of the board and being constructed to set awidth of a gap between the preheater and the solder bath within 20 to 60mm.
 6. The apparatus according to claim 5, further comprising a closingdevice for closing the gap between the preheater and the solder bath soas to prevent a gas stream from passing through the gap.
 7. Theapparatus according to claim 5, further comprising a heating coverlocated above the preheater so as to extend over the board.
 8. Theapparatus according to claim 5, wherein the solder material is alead-free solder material selected from the group consisting of an Sn—Cubased material, an Sn—Ag—Cu based material, an Sn—Ag based material, anSn—Ag—Bi based material and an Sn—Ag—Bi—Cu based material.